Composites

Question 1

What is a composite?

Answer 1

A composite is a material that contains two or more distinct material as a unified combination.

Question 2

How are composites classified?

Answer 2

By a constitution (what the material is made from), reinforcement form, spacial distribution, and relative proportions.

Question 3

What are the types of reinforcement form?

Answer 3

Continuous filament/fibre, Short/discontinuous fibre, Particulate

Question 4

What are the spacial distribution for continuous filament/fibres?

Answer 4

Uniaxial (high volume fraction of reinforcement), woven/ cross stitched (medium volume fraction of reinforcement), swirl mat (varying volume fraction).

Question 5

What are the advantages of composites?

Answer 5

Enhanced and more control over mechanical, physical and chemical properties.

Question 6

What are some possible reason why fibres are strong?

Answer 6

Molecular alignment, Crystallographic alignment, Elimination of flaws, Development of fine structures.

Question 7

What are the main types of fibres?

Answer 7

Glass fibre, Carbon fibres, Polymer fibres and Ceramic fibres.

Question 8

What are the benefits of glass fibres?

Answer 8

Provides good strength properties.

Question 9

What is the difference between pan and pitch carbon fibres?

Answer 9

Pan are cost effective carbon fibres while pitch carbon fibres are highly thermal and electrically conductive.

Question 10

What are the benefits and disadvantages of polyaramid fibres?

Answer 10

They have high stiffness, high toughness and low density but low compression strength and severe degradation in UV.

Question 11

What are the benefits and disadvantages of ceramic fibres?

Answer 11

Handle high temperatures, chemical stable and high stiffness, but generally have a low strength.

Question 12

What are the types of ceramic fibres?

Answer 12

Monofilaments, multifilament, short staple and whiskers.

Question 13

What are monofilaments?

Answer 13

Single continuous strand of fibre.

Question 14

What are multifilaments?

Answer 14

Multiple types of fine strands of fibres twisted together.

Question 15

What are short staple fibres?

Answer 15

Short length fibres

Question 16

What are whiskers fibres?

Answer 16

Very fine single crystal strand of fibres, with both high strength and high stiffness.

Question 17

What are the general properties of fibres?

Answer 17

Fibres tend to be stiffer and anisotropic compared to the bulk counterparts.

Question 18

What is the Weibull distribution?

Answer 18

Since strength is controlled by flaw distribution fibre strength varies on a statistical basis. Shorter length fibres are statistically stronger than longer fibres.

Question 19

What is the polymer matrix?

Answer 19

A continuous phase that protects the fibre, carries shear stress and allows transmission of stress into fibres.

Question 20

What are the processing requirements for a polymer matrix?

Answer 20

Low viscosity, Easy to shape, quality assurance, ideally rapid processing and long pot life.

Question 21

What are the principle thermoset matrices for composites and their benefits?

Answer 21

1) Unsaturated polyester resin, Cheap, limited HT and chemical resistance.
2) Epoxy Resins, more expensive, but better HT and chemical resistance.
3) Vinyl-Ester Resins, intermediate HT and chemical resistance.
4) Phenolic, cheap and moderately mechanical
5) High Temperature Resins, For high temperature resins

Question 22

What are the principle thermoplastic matrices for composites and there benifits?

Answer 22

1) Commodity moulding compounds, medium properties, cheap, good processibility.
2) Thermoformable sheet, more random commodity moulding compounds
3) Engineering thermoplastics, highest strength and HDT
4) High performance thermoplastics, very high Tg

Question 23

What are the advantages of thermoplastics?

Answer 23

Processing is easier to control, recyclability, storage prior to processing, tougher, more moisture resistant.

Question 24

What are the advantages of thermosets?

Answer 24

Lower processing temperatures, faster cycle times, better compression strength, better translation of fibre properties generally more solvent resistant.

Question 25

What is Pultrusion?

Answer 25

Pultrusion is a process that converts fibre reinforcements and resin matrices into finished composite parts. Pultrusion allows for a continuous processing that is easily automated and the production rate are high leading to the systems being very cost effective.

Question 26

What is Prepreg Processing?

Answer 26

When the composite is pre-impregnated continuous fibre reinforcement with partially cured polymer resin

Question 27

What is Filament Winding?

Answer 27

Commonly used to create cylindrical or spherical shapes where a resin is wound around a mandrel then heated and the mandrel is removed.

Question 28

What are Sandwich Panels?

Answer 28

Sandwich Panels are structural composites that consist of two stronger out layers with a less dense inner layer called the core.

Question 29

What is the purpose of the inner layer of a sandwich panel?

Answer 29

The core isn’t only to provide separation for the two plates but they provide a degree of shear rigidity perpendicular to the faces.

Question 30

What is the manufacturing process of pan carbon fibres?

Answer 30

1) PAN fibres spun
2) Hot stretched
3) Oxidised
4) Carbonisation/graphitisation in inert atmosphere

Question 31

What is the manufacturing process of pitch carbon fibres?

Answer 31

1) polymerisation
2) Melt spun
3) Oxidised
4) Carbonised under tension